1. Field of the Invention
The present invention relates to an image forming apparatus utilizing an electrophotographic method, and more particularly to an image forming apparatus such as a copying apparatus, a printer or a facsimile apparatus.
2. Related Background Art
A developing apparatus is conventionally positioned around an image bearing member on which an electrostatic latent image is formed by a primary electrostatic charging device, an exposure apparatus and the like, and cleaning means for removing and recovering a developer remaining on the image bearing member.
In the developing apparatus, there is provided a developer carrying member for causing the developer in such developing apparatus to fly to the image bearing member, and such developer carrying member is provided in a position almost contacting the image bearing member in order to form the electrostatic latent image on the image bearing member into a visible image. On the developer carrying member, there is formed a developer layer of a predetermined thickness by a developing blade. In the developing apparatus, there are provided an agitating member for agitating and carrying the developer toward the developer carrying member, and an antenna member for detecting a remaining amount of the developer.
For the developing apparatus, it is very important to detect the amount of the developer therein. In case the developer is exhausted suddenly, white streaks or white stripes are generated on the image, thereby giving an unpleasant feeling to the user. It is therefore necessary to detect the amount of the developer in the developing apparatus by suitable means and to transmit the result of such detection to the user.
For achieving a compactization of the developing apparatus, a cartridge configuration and a lower running cost, it is desirable to utilize the aforementioned antenna member, rather than a piezoelectric element which converts a pressure of the developer into a voltage.
For a detecting method utilizing such antenna member (hereinafter called antenna method), there is known a method of detecting a voltage induced in the antenna member and comparing the induced voltage with a reference voltage to judge the necessity of the developer replenishment, thereby outputting an instruction.
On the other hand, Japanese Patent Application Laid-open No. 5-35098 proposes a detection method utilizing a developing blade which is capable of detecting the remaining amount with a lower cost, but such method is unsuitable for a more precise detection of the amount of the developer, since this method shows a very large fluctuation in the induced voltage with respect to the developer amount, in comparison with the antenna method.
Also Japanese Patent Application Laid-open No. 8-339118 proposes means for detecting the developer amount in the developing apparatus by a detection method utilizing two reference voltages in the antenna method (hereinafter called 2-step detection method) and forecasting a timing of replenishment.
However, such two-step detection method is associated with a drawback that, in case of rotating an agitating rod and a developing sleeve in order to replenish the developing apparatus with the developer, the agitating rod and the developing sleeve are rotated even in the absence of the developer, thereby resulting in a loss in the density, a deterioration of the developer, an image fog or the like. Also there may result an erroneous display since the copying operation is rendered possible as soon as the second reference signal is reached.